Gas plating apparatus



May 19, 1959 H. J. HOMER ETAL 2,887,089

GAS PLATING APPARATUS Original Filed June 22, 1955 2 Sheets-Sheet 1TINVENTOR. HOWARD J. OMER JOHN R. WHITACRE BY www m ATTO RNEYS UnitedStates Patent GAS PLATIN G APPARATUS Howard J. Homer and John R.Whitacre, Dayton, Ohio, assignors to The Commonwealth EngineeringCompany of Ohio, Dayton, Ohio, a corporation of Ohio Originalapplication June 22, 1955, Serial No. 517,208. Eggs? and thisapplication April 4, 1956, Serial No.

6 Claims. (Cl. 118-48) This application is a division of our co-pendingapplication, Serial No. 517,208, filed June 22, 1955.

This invention relates to the protection and the bonding of metals andis particularly applicable to metals which form surface oxides readilywhen the metal is exposed to the air; oxides thus formed tend to preventthe adherence of protective metal coatings which coatings in manyapplications would be useful in conjunction with such an oxide-formingmetal.

The invention particularly contemplates the joining of metals ofdissimilar characteristics without afiecting desirable physicalproperties of the metals joined. Thus bodies of aluminum metal oraluminum containing alloys which bodies are utilized in manyapplications because of their lightness in weight may be joined to aprotective coating of nickel in such an amount of the latter as tosecure the corrosion and pit resistant characteristics of the nickelwhile substantially retaining the desirable light weight characteristicsof the aluminum.

A particular object of the invention is to provide a method wherebymetals may be joined together without the necessity of time consuming,expensive preliminary de-oxidizing operations.

The practice of this invention includes the steps of providing ametallic interlayer or tie ply between the metals to be joined, theinterlayer consisting preferably of a single metal such as lead. Thelead is adhered to the body of the oxide-forming metal by deposition ofthe lead from a gaseous heat decomposable metal bearing compound at atemperature or temperatures at which the oxide-forming metal isunafiected in physical characteristics; the temperature however ispreferably such that the lead deposit is somewhat plastic. Acorrosion-resistant metal is then applied to the lead preferably also bydeposition from a gaseous heat decomposable metal bearing compound.

The deposition of the lead interlayer is eifected in a non-oxidizingatmosphere and the interlayer as it deposits is itself oxide-free. Leadhowever has an afiinity for oxygen and tends to inter-difiuse with theoxide layer of the oxide-coated metal base and to combine with the oxidelayer to form a bond of high physical properties. The lead is itself,particularly when at a temperature appreaching the plastic condition,receptive to deposits of other corrosion-resistant metals such as nickeland chromium.

In specific application the invention provides for the production ofcladded metal products containing a major portion of aluminum having anon-deoxidized face.

2,887,089 Patented May 19, 1959 principles of this invention.

Such aluminum bodies, when they are formed or are Referring to thedrawingsthere is indicated at 1 in Figure l a hood having therein aheated compartment 3 normally maintained at a temperature of about 275350 F. A second compartment 5 adjacent the first is maintained at atemperature of about 100 F.

Compartment 3 contains a plating chamber 7 which is preferably of Pyrexglass; chamber 7 is provided with a removable sealing closure member 9at its upper end and a sealing closure member 11 at its lower end. Theseobject 23 is suitably suspended by a strap 25 of heat insulatingmaterial from closure 9.

Mounted on the upper outer side of the hood 1 is a steel container 27which retains a supply 29 of tetraethyl lead. Sight glass 31 providesfor viewing the supply. Valve 33 provides for charging the containerthrough conduit 35 and for sealing the supply from the atmosphere.

The container 27 is provided with a pressure gauge 37 and a conduit 39having valves 40 and 41. Conduit 39 is connected to a source of nitrogengas which gas as indicated passes into the hood from the leftward endfrom a supply (not shown) through compartment 5; valve 41 controls theflow of the nitrogen to container 27.

Container 27 is provided also with a conduit 43 having a shut-off valve45 and a flow control valve 47 for metering the flow of liquidtetraethyl lead to conduit 49. Conduit 49 is itself provided with arestricted opening or jet 51 and liquid tetraethyl lead passes the. jetin small drops into a conduit 53 connecting with conduit 49. Mostsuitably the conduit 49 and the jet forming structure are transparentand of Pyrex glass to permit of viewing of the liquid drops by operatingpersonnel.

The conduit 53 is within compartment 3 for a greater part of the conduittraverse and is hence subject to the heat within the compartment, whichheat is maintained at such a level that the flowing tetraethyl leadvaporizes.

The lower end of conduit 53 is provided with a T-connector 55 one arm ofwhich communicates with the plating chamber 7 through piping whichextends through closure; 9. The other arm of the T-connectorcommunicates with chamber 5 and such will be described in detailhereinafter.

Conduit 53 is angled downwardly in hood 1 to permit any liquidtetraethyl lead present to flow; the numeral 59 indicates a pipeconnected to conduit 53 and pipe 59 with valve 60 open is effective topermit liquid to flow to trap 61 which trap consists of a steelcontainer and is provided with a sight glass 63; a coil 65 for passageof water about trap container 61 provides for main- ,taining thematerial passing through pipe 59in a liquid state. Most suitably thetrap is vented through line 67 to a liquid receiver at 69 for absorptionof gases which may pass the trap.

A by-pass line 71 is provided between conduit 39 and jet 51 for the flowof gas through the jet to clean the same; the by-pass is provided withvalve 73 for controlling the gas flow.

Conduit 75 having valve 77 extends through conduit 53 to the pressuregauge 79 and conduit 39. Valve 77 permits of supplying a positivepressure of nitrogen to the lead tetraethyl plating material, as it isvaporized, to carry the plating gas to the chamber 7.

Compartment 3 is maintained at the temperature of about 300 F. in thepresent embodiment by hot air which is blown into the compartmentthrough the duct indicated at 81 in which the electric heaters 83 areincorporated. Thus compartment 3 is a hot air bath in which thevaporizer line 53 and the plating chamber 7 and associated equipment arehoused. A hot air outlet is indicated at 85.

Compartment is also suitably maintained at a temperature of about 75 F.by blowing air as required through a conduit 87. Depending upon theconditions of the surrounding atmosphere the air entering thecompartment 5 may be heated or cooled as required. The air outlet fromcompartment 5 is indicated at 89.

Compartment 5 contains a vaporizer 91 which in this embodiment isprovided with liquid nickel carbonyl, 93. The numeral 95 indicates aflow meter which is connected to the vaporizer by a conduit 97 havingvalve 99 which valve is accessible from the exterior of the compartment.Valve 96 controls nickel carbonyl flow to chamber 7. Piping 101 extendsinto the vaporizer and connects to a source 102 of liquid carbonylthrough valves 103, 105; the source 102 is positioned in any suitablemanner on or adjacent hood 1 externally of the compartment 5. Pressuregauge 104 indicates the pressure in piping 101.

Nitrogen is supplied to vaporizer 91 through conduit 107 and valve 108;conduit 107 supplies conduit 39. Most suitably the nitrogen supplied tothe equipment passes through a flow meter 109 to permit measurement ofthe volume of carrier gas used.

In the practice of the invention the apparatus, with the air baths atoperating temperature, is initially supplied with the tetraethyl lead insufiicient quantity to substantially fill the container 27 and tosubstantially exclude air from the container. The pump 17 is thenoperated with all valves closed except valve 77 and most of the air isthen withdrawn. Nitrogen is then introduced by opening valves 110 and 40and the nitrogen is drawn through the system.

Thereafter, with the low pressure of nitrogen prevailing as indicated bygauge 79, the valves 45 and 41 are opened. A nitrogen pressure thenexists on the tetraethyl lead and valve 47 is cracked open to permit theliquid to flow slowly.

The induction heater coil is preferably brought to a temperature of atleast 600 F. prior to the entry of the flow of the plating gas. Mostsuitably the object 23 has a temperature of 700 F. to 800 F. when theplating gas enters chamber 7.

As the liquid tetraethyl flows to the orifice 51 drops form and thetetraethyl drips into the vaporizer conduit 53; as the tetraethyl movesit is vaporized by the heat from the air bath and the nitrogen flowingthrough conduits 39 and 75 pick up the tetraethyl and carry it intocontact with the aluminum object 23 in the plating chamber.

The aluminum object is preferably cleaned of any surface grit or greaseprior to plating but it need not and suitably is not de-oxidized. Thelead tetraethyl striking the hot aluminum surface decomposes depositinglead. The lead at a temperature of 600 F. is plastic and adheres to thealuminum tenaciously coating the same uniformly. At temperatures between600 F. and 800 F. the lead deposited remains plastic but does not becomefluid despite the fact that in the higher ranges of temperature the leadis above its normal melting point; as a theory the lead and the aluminumor the oxide surface of the aluminum combine to form an intermetallicphase having a higher melting point than the lead. No evidence offluidity appears in the product. However it is to be noted that samplesof lead metal when merely placed on a sample during plating under theconditions of the invention, such lead metal melts and runs oil. Thus anaction takes place when lead is deposited from the gaseous state whichis not present when lead is merely placed on the aluminum and heated tothe same temperature.

Specific operating conditions for the lead deposition are:

Oompart- 'I.E.L Carrier Time of Sample No. ment 3, Sample, Flow, Gas,Run, T., F. 'l., F Drops] c.f.m. Min.

min.

The amount of the deposit in the above examples was least at 600 F. forthe aluminum object and greatest at the higher temperatures and driprates of the tetraethyl. The coatings were however uniform and it is tobe noted that in many instances a very thin coating is to be desiredthatis less than one mil, since the adhesion of the subsequently appliednickel depends upon the character of the deposited lead rather than thequantity. However a thickness of about one mil of lead provides acushion layer which is desirable when the object plated is to be subjectto shock.

Upon completion of the lead deposition valves 41, 45 and 47 are closed,valve 73 is opened and nitrogen is passed through the apparatus to clearthe same of all tetraethyl. At the same time the temperature of thealuminum object is suitably reduced to about 350 F. by limiting theenergy input to the induction coil 21. If desired the temperature of theobject may be maintained constant at 600800 F. during the nickelplating.

Valves 40, 77 and 73 are then closed and valves 96, 99 and 108 areopened to pass nitrogen across the nickel carbonyl in vaporizer 91 tosweep the carbonyl to chamber 7. The combined pressure of the nickelcarbonyl and nitrogen may suitably be much greater than that with thetetraethyl and if desired may approach atmospheric. This permits fasterdeposition of nickel and in general a nickel plating time of about twoto three minutes to deposit one mil thickness of nickel is satisfactory.

The waste products of decomposition of the nickel carbonyl like thewaste products of the decomposition of the lead tetraethyl are drawn offby the: vacuum pump operation. The film of nickel covers the lead and isbright silvery. It may upon removal from the equipment be highlypolished and it serves to protect the aluminum. Further the adhesion ofthe nickel to the lead is excellent.

Argon gas has been substituted for the nitrogen and has provided goodresults. Hydrogen, while it is useful, tends to be highly heatconductive apparently and at high temperatures of the object above 750F. intra-gaseous decomposition tends to occur rendering the depositsomewhat non-uniform.

Chromium hexacarbonyl may suitably be employed as a substitute for thenickel carbonyl but is more expensive. Other carbonyl compounds as wellas the metal hydrides are useful to supply the outer coat but we havefound nickel and chromium to be most satisfactory from an economicstandpoint.

Referring now to Figure 2 the tubular aluminum member 112 is shown tohave on its inner and outer surfaces, a zone coated over-all with a leaddeposit 114; a heavier layer of nickel on the lead is indicated at 116.

Referring now to Figure 3 a flat piece of aluminum 118 is coated withlead at 120 and nickel at 122. Such a piece 4" thick over-all and 6"long may be bent double upon itself without disrupting the bond.

Also a /8" OD. aluminum tube about 6" long, as in Figure 2, when bentdouble upon itself resisted fracture and peeling of the layers.

It will be understood that this invention is susceptible to modificationin order to adapt it to different usages and conditions and accordinglyit is desired to comprehend such modifications within this invention asmay fall within the scope of the appended claims.

We claim:

1. Metallizing apparatus comprising, in combination, means defining acompartment, means defining a chamber located within and separated fromthe compartment for the retention of an object to be metallized, meansdefining a container source above the chamber for the retention of aheat decomposable liquid metallizing agent, conduit means connecting thecontainer and chamber for passing the metallizing agent from thecontainer to the chamber, means to heat and vaporize the liquidmetallizing agent as it passes from the container source through thecompartment to the chamber, means for introducing a carrier gas to thecontainer source to carry the vaporized agent to the chamber,drop-forming orifice means within the conduit means located between thecontainer source and chamber for confining the passage of liquidmetallizing agent to be vaporized to the form of drops of the agent, andinduction heating means associated with the object-retaining chamber forthe heating of an object to the decomposition temperature of themetallizing agent.

2. Metallizing apparatus comprising, in combination, means defining acompartment, means defining a chamber located within and separated fromcompartment for the retention of an object to be metallized, meansdefining a container source above the chamber for the retention of aheat decomposable liquid metallizing agent, conduit means connecting thecontainer and chamber for passing the metallizing agent from thecontainer to the chamber, means to heat and vaporize the liquidmetallizing agent as it passes from the container source through thecompartment to the chamber, means for introducing a carrier gas to thecontainer source to carry the vaporized agent to the chamber,drop-forming orifice means within the conduit means located between thecontainer source and chamber for confining the passage of liquidmetallizing agent to be vaporized to the form of drops of the agent, andinduction heating means associated with the objectretaining chamber forthe heating of an object to the decomposition temperature of themetallizing agent.

3. Metallizing apparatus comprising, in combination, means defining acompartment, means defining a chamber located within and separated fromthe compartment for the retention of an object to be metallized, meansdefining a container source for the retention of a heat decomposableliquid metallizing agent, conduit means connecting the chamber andcontainer, said conduit means having therein drop-forming restrictedorifice means for the passage of liquid metallizing agent from thecontainer towards the chamber in drops, the container source beingpositioned above the chamber for gravity flow of the liquid metallizingagent and said conduit means providing a long angled flow path for. themetallizing agent, means to heat and vaporize the drops of liquidmetallizing agent as they pass through the compartment means from thecontainer source to the chamber, means for introducing a carrier gas tothe container source to carry the vaporized agent to the chamber, andinduction heating means associated with the object-retaining chamber forthe heating of an object to the decomposition temperature of themetallizing agent.

4. In metallizing apparatus, in combination, means defining acompartment, means defining a chamber located within and separated fromthe compartment for the retention of an object to be metallized, meansdefining a container source for the retention of a heat decomposableliquid metallizing agent, conduit means connecting the container andchamber for passing the metallizing agent from the container to thechamber, said means including first conduit means leading out of thecontainer for the flow of liquid metallizing agent therefrom, otherconduit means extending into the top of the container and adapted forthe passage of gas into the container for effecting a pressure thereinto occasion flow of liquid agent to said first conduit means, meansWithin said first conduit means defining a drop-forming orifice locatedbetween the container source and the chamber for limiting the flow ofliquid metallizing agent to the form of drops, electric heating means toheat and vaporize the drops of liquid metallizing agent as they passfrom the container source through the compartment means to the chamber,means for introducing a carrier gas to the container source to carry thevaporized agent to the chamber, and induction heating means associatedwith the object-retaining chamber for the heating of an object to thedecomposition temperature of the metallizing agent.

5. Metallizing apparatus comprising means defining a compartment andlocated within the compartment a chamher for the retention of an objectto be metallized, the interior of the chamber being closed off from thecompartment, a conduit leading into the chamber and passing over aportion of its length through the compartment for the supplying of ametallizing agent to the chamber, a container source for the retentionof the liquid metallizing agent, induction heating means within thecompartment surrounding the chamber, means for exhausting said chamberof gases therein, means defining a restricted, drop-forming orificeleading into said conduit for the passage of drops of liquid metallizingagent through said conduit towards said chamber, means for heating theatmosphere of the compartment in the vicinity of the portion of theconduit passing therethrough for effecting volatilization of liquid inthe passage thereof, and means for introducing a carrier gas into thecontainer source to carry the vaporized agent to the chamber.

6. Metallizing apparatus comprising means defining a compartment andlocated within the compartment a chamber for the retention of an objectto be metallized, the interior of the chamber being closed off from thecompartment, a conduit leading into the chamber and passing over aportion of its length through the compartment for the supplying of ametallizing agent to the chamber, a container source for the retentionof the liquid metallizing agent, induction heating means within thecompartment surrounding the chamber, means for exhausting said chamberof gases therein, means defining a restricted, drop-forming orificeleading into said conduit for the passage of drops of liquid metallizingagent through said conduit towards said chamber, means for heating theatmosphere of the compartment in the vicinity of the portion of theconduit passing therethrough for effecting volatilization of liquid inthe passage thereof, means for introducing a carrier gas into thecontainer source to carry the vaporized agent to the chamber, and meansfor drawing ofi from the conduit unvolatilized liquid to prevent thepassage thereof to the chamber.

References Cited in the file of this patent UNITED STATES PATENTS287,318 Perkins Oct. 23, 1883 2,516,058 Lander July 18, 1950 2,619,433Davis et a1. Nov. 25, 1952 2,657,152 Mengali et a1 Oct. 27, 19532,671,739 Lander Mar. 9, 1954

